Production of piezo-electric elements



Feb. 4, 1930. J. H.-CHRISTOPHER 1,746,144-

PRODUCTION OF PIEZO ELECTRIC ELEMENTS Filed March 8, 1,927

Inventor John H-.Christopher,

fg/W His Attorneg.

Patented Feb. 4, 1930 UNITED JOHN H. CHRISTOPHER, 0F SCHENEGTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIC COMPANY, A CORPORATION OF NEW YORK PRODUCTION PIEZO-ELEGTRIC ELEMENTS Application filed March 8, 1927. Serial No. 173,753,

My invention relates to the production of piezo electric elements, such as Rochelle salt crystals or the like, and has for its principal object the provision of an improved method and apparatus whereby the production of sion waves set up in it when it is subjected to the electrical stress of an alternating elec trostatic field. It has heretofore been customary to out such blocks from the complete crystal inknown relation to the optical and electrical axes of this crystal. of production requires that the natural crystal be cut into plates or slabs which have theirfaces parallel with certain of the crystal faces and that the blocks be cut from these slabs at a definite angle to the, edges of the slab.

' In accordance with my invention, the production of piezo electric elementsis greatly facilitated by growing the crystal in the form of a plate or slab with the crystal material oriented in the slab in the same manner as it would be if out from a complete crystal in the usual manner. Thisis accomplishe by cutting a seed crystal from a portion f a perfect crystal in such a way that one 10f its faces is parallel to a certain face of the complete crystal and placing this face of this seed crystal against one of twoplates spaced apart byspacers having the thickness which it is desired that the finished crystalslab shall have. Thecrystal slab is then caused to grow by the method set forth in Letters Patent of l the United States of Roy W. Moore, No.

1,347,350, July 20, 1920, or in any other suit able manner, In this way the crystaLis confined between the plates and can only row into a slab of the required thickness. the seed is cut with the crystal material ori- This method growth is to be produced.

inceented as desired-and the crystal slab follows this orientation. in its growth, the result is a crystal slab which is similar to that cut from a complete crystal and which may cut into blocks in the usual manner.

My invention will be better understood from the following description when consid- I ered in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

Referrin-g to the drawings, Figs. 1 and 2 illustrate various-features of an apparatus adapted to grow crystals in accordance with my invention; and Figs. 3 and i are plan and perspective views of a Rochelle salt crystal. As pointed out in the aforesaid Letters Patent, crystals of various substances may be produced by controlling the temperature of the solution or motherliquor to produce and maintain a slight degree of supersaturation.

By thus carefully 'maintaining the degree of supersaturation below the point of irregular crystallization, perfectly developed, clear crystals of large size are formed, and these crystals continue to grow clear and perfect so long as a suitable state of supersaturation is maintained. 2

Fig.1 showsa receptacle 1 which contains a solution 2, is located within a tank 3, and is surrounded by a suitable bath 4: which serves as a'heat reservoir for stabilizing the temperature of the solution 2 wherein the crystal A heating element, shown as 'a coil 5 is; provided for con trolling the temperature/of the bath 4, this coil being supplied from a source Q with heating current regulated by means comprising a thermostatic element 7, a source 8s'and a re, lay switch 9 which interrupts the heating current in response to apredetermined tem+ perature of the bath 4 It wi i be observed that receptacle 1 is mounted o a support 10;

and that 'a plurality of plates 11 separated by spacers 12 are immersed in ti 1e crystal forming solution 2 which may be Rochelle salt (sodium potassium tartrate) Zor any other I i k I V I i Figs. 3 and 4 which 'illustrate a typical Rochelle salt crystal with itsfaces lettered in the usual manner. It will be observed that the a, b and c faces are mutually perpendicular. Having located these faces, a slab 13 of suitable thickness is cut perpendicular to the c and b? faces and parallel to the a, face. The elements or blocks are then cut from the slab 13 by cutting perpendicular to the a face and either parallel or at any suitable angle with b and a faces. In Fig. 4, the blocks are indicated by dotted lines as cut with faces which make angles of 45 with the b and 0 faces.

In accordance with the present invention, seed crystals are cut with one face parallel with the a face of the complete crystal and these seed crystals are placed in the solution 2 between the plates 11 with their a faces in contact with the lower plate as indicated by dotted lines at 14 in Fig. 2. Under these conditions, these seed crystals are forced to grow in the form of a slab 15 which is similar in all respects to the slab cut from the complete crystal as described above, and the piezo electric elements or blocks may be cut from this slab in the usual way. It will be readily understood that the production of piezo electric elements is thus greatly facilitated due to the fact that no cutting in planes parallel to the a face of the complete crystal is required.

The embodiment of the invention illustrated and described herein has been selected for the purpose of clearly. setting forth the principles involved. It will be apparent, however, that the invention is susceptible of being modified to meet the difierent conditions encountered in its use and I therefore aim to cover by the appended claims all modifications within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The method of producing a piezo electric element, Which comprises cutting a seed erystal with a face parallel to a face of the complete crystal from which it is taken, and

placing said seed in a crystal growing solution v with said face parallel to and between plates spaced apart by a distance which is equal to the desired thickness dimension of said element.

2. The method of producing a piezo electric element, which comprises cutting a seed crystal with a face parallel to a face of the complete crystal from which it is taken, placing said seed in a crystal growing solution with said face parallel to and between plates spaced apart by a distance which is equal to the desired thickness dimension of said element, and maintaining said solution in a slightly supersaturated state.

3. The method of producing a piezo electric element, which comprises cuttinga seed crystal with a face parallel to the a face of the complete crystal from which it is taken, and placing said seed in a crystal growing solution with said face parallel to and between members spaced apart by a distance which is equal to a desired dimension of said element.

In Witness whereof, I have hereunto set my hand this 7th day of March, 1927.

J OHN H. CHRISTOPHER. 

